Tips for Optimizing Shell Scripts for Better Performance

Shell Programming and Scripting
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Tips for Optimizing Shell Scripts for Better Performance

Hello Unix enthusiasts,

As someone who’s constantly working with shell scripts for automation, I've picked up a few tips to optimize script performance. I wanted to share them here and get your thoughts or additional suggestions!

  1. Avoid unnecessary processes: Minimize the use of external commands like sed, awk, or grep when built-in shell capabilities like parameter expansion or case statements can do the job.
  2. Use $(...) instead of backticks: Substituting commands with $() is not only more readable but also allows for easier nesting of commands.
  3. Leverage arrays: Instead of looping through files or strings with traditional methods, arrays can speed things up significantly in bash or ksh scripts.
  4. Redirect output efficiently: If you need to append data to a file multiple times, open the file once and redirect output instead of repeatedly using >>.
  5. Enable debugging when testing: Use set -x or bash -x script.sh to trace and understand where the script might be slowing down.

What are some tricks or practices you use to make your scripts more efficient? Let's discuss shakeys and learn from one another!

Looking forward to your insights!

Cheers,

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Welcome @oscar2, this is a good summary.
My 2cents:

1.+ Use an external command only if you do much with it: process a big file, do multiple operations.

3.+ A Parameter Expansion can be applied on all array members without a loop. For ex. printf "%s\n" "${array[@]%.*}" removes a .* extension from each member. Can be assigned again: array=( "${array[@]%.*}" ).

6. Avoid cat. Bad examples are widespread. cat filename | is simply < filename. pid=$(cat pidfile) is simply read pid < pidfile.
Annotation: in the old Bourne shell builtins like read could end the script if not successful, so the cat workaround was established. Newer shells don't need a workaround.

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